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Soybean Growers Should Be Watching For Soybean Leaf Defoliation

Nebraska soybean growers may be noticing soybean defoliation in their fields. The culprit is most likely grasshoppers and/or bean leaf beetles, University of Nebraska-Lincoln (UNL) specialists say.

Numerous reports have come in about grasshopper populations building along field edges and bean leaf beetle populations building in some areas of the state, mainly in the south, says Tom Hunt, UNL entomologist at the Haskell Agricultural Laboratory near Concord.

Defoliation is the most common type of insect injury observed by Nebraska soybean growers and can occur from emergence to harvest, he said.

While there are several insects that defoliate soybeans in Nebraska, such as the bean leaf beetle, imported long-horned weevil, grasshopper, woollybear caterpillar, thistle caterpillar, green cloverworm and a few others. Rarely does any single species do enough harm to cause economic damage, says Keith Jarvi, UNL Extension educator in Dakota, Dixon and Thurston counties.

"However, the combined injury of two or more defoliating insects can result in economic damage," Jarvi says.

In 1997, entomologists observed combined defoliation from grasshoppers and bean leaf beetles that reached 50% in reproductive-stage soybean near Mead.

"When this occurs, soybean growers need to take several things into consideration," Hunt says.

More information, including specific recommendations, is available in the latest edition of Crop Watch, UNL Extensions crop production newsletter.

"When it comes to treatment and pest-management decisions, a crucial consideration is the size of the remaining soybean canopy and the stage of growth the soybeans are in," Hunt says.

If treatment is warranted, identify the defoliating insect or insects and use the insecticide guides found at Entomology Department. Most commonly used foliar insecticides are effective against most soybean defoliators.